1. Field of the Invention
The present invention relates to a switch module configured to receive and transmit a plurality of communication signals using a common antenna.
2. Description of the Related Art
In recent years, a communication apparatus has come to transmit and receive a plurality of communication signals in different frequency bands using a common antenna, as cellular phones and the like have come to use multiple bands (refer to, for example, Japanese Unexamined Patent Application Publication No. 2008-10995). As a result, a communication apparatus has increasingly utilized a switch module that connects a plurality of communication circuits to a common antenna through switching.
FIG. 6A is a block diagram illustrating a general circuit configuration of a switch module.
A front-end circuit FEC illustrated in FIG. 6A includes a switch circuit SW, a common-terminal-side circuit 104, and switching-terminal-side circuits 107A to 107H. The switch circuit SW is configured to be capable of switching among ports PIC11 to PIC18 so that one of them is connected to a common port PIC01. The common-terminal-side circuit 104, which is connected between an antenna and the common port PIC01 of the switch circuit SW, is configured to function as both an electrostatic damage protection circuit and a matching circuit in this case. The common-terminal-side circuit 104 may be configured as, for example, a coupler, a filter circuit, a stand-alone matching circuit, or a stand-alone electrostatic damage protection circuit, or as a complex circuit which is a combination of these functions. The switching-terminal-side circuits 107A to 107H are provided between the communication circuits of respective communication systems and the respective ports PIC11 to PIC18 of the switch circuit SW. Here, the switching-terminal-side circuit 107A is a low-band-side transmission filter, the switching-terminal-side circuit 107B is a high-band-side transmission filter, and the switching-terminal-side circuits 107C to 107H are transmission lines. Note that the switching-terminal-side circuits 107A to 107H may be configured as transmission filters, reception filters, duplexers, capacitors, transmission lines, and the like.
The front-end circuit FEC described above is usually formed as a switch module which includes a multilayer substrate. The circuit devices of the switch circuit SW, the circuit devices of the common-terminal-side circuit 104, the circuit devices of the switching-terminal-side circuits 107A to 107H, and the like are formed of surface-mount components which are surface-mounted on the multilayer substrate, electrode patterns which are formed on the top surface and the bottom surface of the multilayer substrate and inside the multilayer substrate, and the like.
FIG. 6B is a schematic sectional view of an existing configuration example of a switch module.
A switch module 101 illustrated in FIG. 6B forms the front-end circuit FEC and includes a multilayer substrate 111 and chip devices 121A to 121C. The multilayer substrate 111 includes connection wiring lines 112, an inner-layer ground electrode 113, device mounting electrodes 114, and external connection electrodes 115. The external connection electrodes 115 are electrodes for mounting the switch module 101 on an external substrate. The device mounting electrodes 114 are electrodes for mounting the chip devices 121A to 121C and are connected to the inner-layer ground electrode 113 and the external connection electrodes 115 through the connection wiring lines 112. The inner-layer ground electrode 113 is connected to a ground potential through the external connection electrode 115. Note that the chip device 121A is a circuit device which forms the switch circuit SW. The chip device 121B is a circuit device which forms the common-terminal-side circuit 104. The chip devices 121C are circuit devices which form the switching-terminal-side circuits 107A to 107H.
The switch module 101 with an existing configuration has the following problems.
First, undesired coupling through the inner-layer ground electrode 113 is generated within the common-terminal-side circuit 104 as a result of the chip device 121B forming the common-terminal-side circuit, and the connection wiring lines 112 connected to the chip device 121B being connected to or arranged close to the inner-layer ground electrode 113.
Second, as a result of the chip device 121C forming the switching-terminal-side circuit, and the connection wiring lines 112 connected to the chip device 121C being connected to or arranged close to the inner-layer ground electrode 113, undesired coupling through the inner-layer ground electrode 113 is generated between the chip device 121C and the chip device 121B connected to or arranged close to the inner-layer ground electrode 113.
These couplings, which degrade isolation characteristics among the chip devices, cause degradation in the characteristics of the front-end circuit FEC.